Flexure arrangements

ABSTRACT

A flexure arrangement, suitable for use with or as part of, e.g., an optical beam steering arrangements, and intended for supporting and transmitting movement to any appropriate element, the arrangement including a first flexure to which movement is applied, a second flexure which attaches the arrangement to any appropriate supporting structure, structure linking the first flexure to the second flexure and structure for receiving any appropriate element, the first and second flexure being appropriately spaced so that any movement applied to the first flexure is amplified by the flexure arrangement.

BACKGROUND TO THE INVENTION

The present invention relates to flexure arrangements, suitable for usewith or as part of e.g. an optical beam steering arrangement, andintended for supporting and transmitting movement to any appropriateelement.

The closest prior art known to the applicant is disclosed inPCT/GB01/00062 which is one of the applicant's own patent applications.

One of the objectives of the invention is to further improve beamsteering arrangements which are capable of being assembled to formoptical switches with a large number of input and output ports whilebeing of minimal sizes. The invention aims therefore to further improvethe compactness of beam steering arrangements.

Another objective of the invention is to render the arrangements simpleto manufacture and assemble. In order to achieve this, reducing thecomplexity of an optical switch is an important consideration.

A further objective of the arrangements with which this invention isconcerned is to provide an even further accurate steering facility toachieve higher quality switching.

A particular objective of the inventive arrangements is to achieve agreater angular swing of any element destined to be displaced by thearrangements which is far greater than the movement applied to thearrangement. Achieving an enhanced scale of amplification of movementwill be an important factor in achieving the objective of compactnessmentioned above.

Other considerations such as longevity and costs are also taken intoaccount in the design of these arrangements.

One of the objectives of this invention is to provide a reduction of thebeam actuators length as compared to the prior art system.

A further objective of the invention is to offer a new approach toproviding the orientation and support of an optical element such as acollimator while achieving the required high level of accuracy and longterm dependability.

An additional aim of the current invention is to improve the assembly ofany individual components to the arrangement, thus rendering thearrangement altogether more practical.

A further objective of this invention is to present an improved kind oftwo dimensional (2D) piezoelectric actuator.

SUMMARY OF THE INVENTION

In its broadest independent aspect, the invention presents a flexurearrangement, suitable for use with or as part of e.g. an optical beamsteering arrangement and intended for supporting and transmittingmovement to any appropriate element, the arrangement comprising a firstflexure means to which movement is applied, a second flexure means whichattaches the arrangement to any appropriate supporting structure, meanslinking said first flexure to said second flexure and means forreceiving any appropriate element, the first and second flexure beingappropriately spaced so that any movement applied to said first flexuremeans is amplified by the flexure arrangement.

This arrangement is particularly advantageous in terms of amplifying themovement of the element when received by said receiving means. It alsohas advantageous vibrational and balancing properties.

In a subsidiary aspect in accordance with the broadest independentaspect of the invention, the flexure means are essentially parallel withrespect to one another.

This particular feature is advantageous because it improves themechanical properties of the arrangement.

In a further subsidiary aspect, the element is an optical element.

It is well known that precision is an essential requirement of opticalcommunication systems, bearing this in mind, the advantages of thearrangement come to light in this particular application, because itsimplementation yields enhanced precision.

This structure has the particular benefits of improving theanti-vibrational characteristics of the arrangement, and of allowing themoments of inertia of the elements operating with the arrangement to beadvantageously balanced.

In a further subsidiary aspect, the element is a collimator.

Due to the inherent shape of the collimator (usually being an elongaterod), the advantages of employing such an arrangement are particularlypertinent.

In a further subsidiary aspect, the first and second flexure means arespaced at a distance less than half the collimator's length. This allowsadvantageous amplification to occur when the element is a collimator.

In a further subsidiary aspect, the element is a reflective.

Some of the advantages put forward with regard to optical elementsgenerally, are particularly pertinent to this configuration.

In a further subsidiary aspect, the element is a grating.

Similarly, to the previous configuration, using the flexure arrangementwith a grating yields some of the advantages put forward with regard tooptical elements generally.

In a further subsidiary aspect, the invention presents a beam steeringarrangement, comprising a flexure arrangement in accordance with thebroadest independent aspect, a collimator being the element with whichit operates and actuating means for applying movement to the firstflexure means, so that an actuator movement in any direction causes acollimator movement in the opposite direction, the relative moment ofinertia of the actuator and collimator acting to counterbalance anyexternally induced movements.

In a further subsidiary aspect, the actuating means is a piezoelectricactuator which when actuated displaces two dimensionally. This featureis particularly advantages because it allows a lateral movement of theactuator to occur which is transmitted to the element as amplifiedangular motion.

In a further subsidiary aspect, the first flexure means is locatedupstream from the second flexure means. This provides the arrangementwith advantageous mechanical properties.

In a further subsidiary aspect, any of the arrangement's componentsincorporate a slot extending from the periphery to an inward portion ofsaid components, thereby facilitating the ready insertion and/or removalof an optical fibre.

This latest aspect of the invention is deemed to be particularlyadvantageous because it avoids having to thread an optical fibre througha series of apertures along the Z axis. This in turn enables a fibre tobe rapidly inserted into the various components of the steeringarrangement. Therefore, this aspect significantly simplifies theassembly of the steering arrangement.

In a further subsidiary aspect, any of the flexure means comprises ahole sufficient in diameter to allow the passage of an optical fibre andto avoid contact between the fibre and the or each of said means.

This is particularly advantageous because it avoids unwanted stressconcentrations along the fibre itself at the flexure points where suchstress concentrations could otherwise lead to premature fracture.

In a further subsidiary aspect, the support structure is an actuatingmeans. This is particularly advantageous because it may render thearrangement altogether more compact.

In a subsidiary in accordance with the broadest independent aspect, thearrangement extends in the Z-direction, comprising at least a first andsecond actuating means, the first flexure means being at least in partthe extremity of said first actuating means which extends in theZ-direction when actuated and the second flexure means being meanslocated at the extremity of said second actuating means, thereby whenthe first beam is actuated, the collimator pivots.

The advantages of the arrangement of the preceding aspects areaccentuated when the arrangement is incorporated in an optical switch

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a beam steering arrangement.

FIG. 2 shows a perspective view of the support structure with itsactuator mounted therein.

FIG. 3 presents a perspective rear view of the mount.

FIG. 4 shows a perspective rear view of the piezoelectric actuator, theoptical fibre, the mount and a partial view of the collimator.

FIG. 5 presents a perspective view of an input or output array of aswitching system.

FIG. 6 shows an optical switch system of a further embodiment of thepresent invention.

FIG. 7 shows a perspective view of a mount in accordance with a furtherembodiment of the present invention.

FIG. 8 shows a schematic perspective view of a further embodiment of thepresent inventive arrangement.

FIG. 9 shows a schematic perspective view of a further embodiment of thepresent inventive arrangement.

FIG. 10 shows a schematic perspective view of a further embodiment ofthe present inventive arrangement.

DETAILED DESCRIPTION OF THE INVENTION

The device presented on FIG. 1 is designed to accommodate a singleoptical fibre and can be used interchangeably either as an input port oran output port in the context of either an input array or an outputarray.

The main components that constitute the beam steering arrangementpresented in FIG. 1 are a support structure 1, an actuator 2, a flexurearrangement 3, a collimator 4 and an optical fibre (not shown in FIG.1). The entire beam steering arrangement shown generally at 5 isparticularly well adapted to be inserted into an optical switchingsystem (described in more detail at a later stage in this patentapplication).

FIG. 2 presents a support structure 21 with only the actuator 22. As canbe seen on surface 24 the support structure, when viewed in crosssection is L-shaped. The external sides of the L are preferably of equallength and measure approximately 4 mm. The actuator 22 takes the form ofa beam whose cross-section measures approximately 1.8×1.8 mm. It isclamped to the support structure at one extremity over a length ofapproximately 10 mm. The unsupported length of the beam is of 31 mmwhich results in an overall length for the piezoelectric actuator of 41mm. There are also clearances between the beam 22 and the supportstructure 21 to allow the necessary displacement of the beam in anysideways direction and up and down. The piezoelectric actuator 22 isformed of layer of electrodes and piezoelectric material extending inthe longitudinal direction and arranged so that there are no hollowportions through the actuator in order to be as compact as possible. Theelectrode and corresponding piezoelectric-layers are placed along theactuator essentially parallel to one another but divided in fourseparate portions of action to achieve bend in the X and Y directions.

FIG. 3 presents at 31 a flexure arrangement viewed in perspective fromthe support structure side. The collimator receiving means 32 isprovided with a bore 33 sufficient in diameter to receive an extremityof the collimator (not shown in the figure). While the diameter of thebore 33 can be selected to immobilise the collimator, additional meansof attachment such as an epoxy resin may be employed to further securethe collimator to the mount 32. The inner face of mount 32 receives theextremities of flexures 34 and 35. These flexures are arrangedorthogonal to each other and along the X and Y axes respectively.

Flexure 34 is attached at one of its extremities to the inner face 36 ofthe mount 32, while flexure 35 is attached at one of its extremities tostep 37 which acts as part of the linking means defining the gap betweenflexure 34 and flexure 35. The means to fix the flexures to the mount 32will be selected from known alternatives by the person skilled in theart.

These flexures are preferably 2.4 mm long, 1.2 mm wide and 0.025 mmthick. The material employed for these flexures is preferably BerylliumCopper which is an ideal selection for the purpose of these flexures dueto the ductility of this material. An alternative preferred material iselectroformed nickel. The separation between the flexures isapproximately 0.75 mm.

The flexures are designed to bend (be compliant) in both flexure andtorsion modes, and resist bending in both compression/stretch along thelength and shear across the length. These properties allow the flexuresto be located close together to constitute an efficient high gain 2Dposition to angle converter.

The position to angle gain of the structure is set by the gap betweenthe flexures—i.e. a gap of 1 mm gives a gain of 1000 radians outputangle per m of input travel. An efficient converter is one where only asmall amount of mechanical energy is stored in the flexures when theyflex and/or twist, thus avoiding unnecessary reduction in travel due tothe finite stiffness of the input actuator, and where thestretch/compression and shear displacements of the flexures are alsovery small compared to the travel of the input actuator.

These second effects are especially important, as not only do theydirectly detract from the available input displacement, they alsodetermine how close to the primary resonance of the structure (definedprimarily by the stiffness of the input actuator and the mass of themoving parts) unwanted secondary resonances occur.

A well designed system will have secondary resonances 6 to 10 timeshigher than the primary resonance, the higher this number the cleanerthe open loop response of the actuator, and the more tightly theactuator can be controlled in a feedback loop.

The magnitude of these effects is strongly driven by the position toangle gain aimed for—as the gain is increased (by moving the flexurescloser together) the force to generate a given output torque (eitherstatic or to overcome angular inertia of the output device orcollimator) increases; but also the change in output angle from anycompression/stretch or shear of the flexures in response to these forcesalso increases. Hence to maintain the same degree of loss of output orfreedom from unwanted resonances as the gain is increased requires theresistance of the flexures to undesired distortion to increase as thesquare of the desired gain.

Returning to the specific description of FIG. 3, both flexures areprovided with a central hole with a diameter of approximately 0.6 mmwhich can easily accommodate the fibre without the fibre coming intocontact with the edges of the holes 38, particularly when the fibre isan SMF28 (single mode fibre 28) with a 250 μm acrylic jacket.

The fibre serves a mechanical purpose in the structure as well ascarrying the light. It provides a constraint in the Z axis on thecollimator, which otherwise would be free to move via the flexuresdeflecting in an S-shape. Provision of this constraint avoids a lowfrequency resonance form in this displacement mode.

The location of the fibre through the centre of the flexures means thatthe flexures are three or more times stiffer in resisting unwanteddistortions from static and/or dynamic forces on the outputdevice/collimator. This is because the flexures are prone to twist ifthe centre of the output load does not run along the centre line. Incertain circumstances it may not be practical to do this, and the fibreshould be placed beside (and as close as possible to) the flexures.

Flexure 34 incorporates at one extremity means to attach the flexure tothe frame or support structure of the type which was described in detailwith reference to FIGS. 1 and 2. These particular attachment meanscomprises an extension member 39.

With regards to flexure 35, it comprises at one of its extremities meansto attach the flexure to the actuator (not illustrated in this figure).

FIG. 4 shows in detail how the flexure arrangement described in FIG. 3attaches to the free end of the actuator 41. This figure also shows theoptical fibre 42 extending parallel to the actuator 41 and passingthrough both flexures to terminate in the collimator which can only bepartly viewed in this figure. The means employed to fix the opticalfibre 42 to the actuator 41 are provided and illustrated at 43. Thesemeans of attachment are preferably an epoxy resin of the type whichwould guarantee a reliable attachment between the fibre and the actuatorthrough the numerous flexure cycles during the life of the beam steeringarrangement. The optical fibre is preferably glued to the actuator 3 mmbefore the closest flexure and preferably terminates in the collimator 1mm past the flexure furthest from the actuator.

The configuration discussed above with reference to FIGS. 1-4 isparticularly advantageous because it has as its effective pivot for thecollimator, the flexure which is fixed to the frame. This permitsmovement of the collimator about the X and Y axes which are orthogonalto the Z axis, the Z axis being the beam forming axis of the collimator.Since this collimator pivots about that particular point, anadvantageous beam swing can be obtained in operation while thetranslational movement of the collimator remains constrained.

Another advantageous mechanical property lies in the fact that while theactuator is displaced under the application of one or more drivesignals, the actuator will bend in one direction causing the collimatorto tilt in the opposite direction. This yields inertial balance,eliminates mechanical cross-coupling between multiple devices mounted tothe same structure, and removes sensitivity to external vibration. Thistype of symmetry is particularly useful in eliminating the resonancesand harmonics that are often troublesome with densely packed mechanicalcomponents operating at high frequencies. This configuration also hasuseful damping properties which further improve the quality andreliability of this particular beam steering arrangement.

FIG. 5 shows an array of beams steering arrangements incorporating aflexure arrangement or mount of the type described above and disposed asa radial array. The longitudinal axis of the actuators in each slice 50is directed substantially towards the central actuator of an opposingslice in an opposing array (not illustrated in FIG. 5). Such aconfiguration minimises the need for additional deflection from opticalsystems in their deflection region referenced generally at 51. Anadditional advantage of this configuration is that a smaller range ofangular movement at the collimator will suffice to steer a beam from anypossible input to any possible output.

The array shown generally at 53 comprises 36 beam steering arrangementsin a common support structure. Each collimator 52 can have 1.25 mmdiameter, 1.65 mm diameter metal housing and be 10 mm long. The metalhousing of the collimator should facilitate operation in conjunctionwith capacitive sensing means. These capacitive sensing means can be asillustrated in FIG. 5 incorporating housings 55 within which thecollimator displaces and sensor plates 54 disposed at the free end ofthe collimator. These plates can be arranged to sense the movement ofthe end of the collimator in both the X and Y direction.

The position measurements obtained through these capacitive sensors canthen be fed back into the switch systems control means.

A variation of these capacitive sensing means is illustrated in FIG. 6which shows an input and output array for the switch system 60. Eachslice of beam steering arrangements operates with a sensor board 61which incorporates holes of approximately 3.4 mm square which carrysense electrodes on their sides. These sensor boards are about 1 mmthick. The capacitance to collimator (at the centre position) from eachelectrode is 0.025 pf. The sensitivity of the north/south capacitors (orthe east/west capacitors) to the displacement at the centre point isapproximately 0.05 ff/μm. Each centre of sensor board is placed atapproximately 6.5 mm from the effective pivot of the collimator which isas discussed previously the flexure fixed to the frame.

FIG. 7 illustrates a further embodiment of the flexure arrangement ofthe present application. The arrangement 70 comprises a collimatorreceiving means 71 in the form of a central bore which incorporates aslot 72 extending from the periphery to an inward portion of thereceiving means. The slot 72 is sufficiently wide to allow the passageof an optical fibre.

The flexures 73 and 74 also have a slot extending from their peripheryto an inward portion. These slots are preferably inline with slot 72 soas to even further simplify the assembly of the optical fibre andcollimator to the arrangement 70. In order to achieve this, the flexureplates 73 and 74 have been disposed in parallel while their attachmentmeans are adapted to achieve similar properties to the flexurearrangement illustrated in FIG. 3 which does not comprise any slots.

FIG. 8 presents a further flexure arrangement 75 comprising a firstflexure 76 and a second flexure 77 both attaching collimator 78 at oneextremity and their respective actuators 79 and 80. The attachment meansof the actuators and the optical fibre have been omitted from the figurefor clarity. Both actuators may be one-dimensional piezoelectricactuators such that for example when the actuator 80 is displaced in theX direction, the actuator 79 acts as the support structure of thepreceding embodiments so that the collimator pivots and has an angularswing in the opposite direction to the movement of the actuator 80.

If both actuators 79 and 80 are actuated simultaneously or only actuator77, the flexure and the collimator move in the same direction, thus thearrangement does not provide in this mode of operation the balancing ofthe kind obtained in the previous embodiments.

FIG. 9 presents a flexure arrangement 81 as integrated in an opticalbeam steering arrangement 83 terminating in a collimator 82. The beamsteering arrangement 83 is provided with a number of actuators 84terminating in flexures such as that referenced 85. The actuators 84 maybe piezoelectric-actuators which flex in the Z direction when actuated.When any of the actuators is flexed but one of the others at least isnot actuated or not actuated to the same degree, the collimator pivots.The supporting structure of at least one of the flexures is in thisembodiment at least one of the actuators.

FIG. 10 illustrates a further flexure arrangement generally referenced86 comprising one dimensional actuators 87 and 88 of the type describedwith reference to FIG. 8. Additional flexures 89 and 91 are providedbeing joined together at one extremity by a spacer 90 and fixed to theirrespective actuator at the other extremity. The spacer 90 engagesflexure 92 which is of the kind described with reference to FIGS. 1 to7. This arrangement is particularly advantageous in terms of achievingvibrational balance in both axes whilst employing one-dimensionalactuators.

The flexure arrangements of the preceding embodiments were described asoperating with a collimator. The inventive flexure arrangement mayoperate with other optical elements such as for example: deflectiveelements and gratings and is intended for use in any application where aflexure arrangement is required to support any appropriate element andtransmit movement to any appropriate element—the scope of the inventionbeing defined in the claims that follow.

1-16. (canceled)
 17. A flexure arrangement, suitable for use with or aspart of an optical beam steering arrangement, and intended forsupporting and transmitting movement to any appropriate element, thearrangement comprising: a first flexure to which movement is applied; asecond flexure which attaches the arrangement to any appropriatesupporting structure; means for linking the first flexure to the secondflexure; and means for receiving any appropriate element, wherein thefirst and second flexure are non-coplanar and appropriately spaced,whereby any movement applied to the first flexure is amplified by theflexure arrangement.
 18. An arrangement according to claim 17, whereinthe first flexure and the second flexure are substantially parallel withrespect to one another.
 19. An arrangement according to claim 17,wherein the element is an optical element.
 20. An arrangement accordingto claim 17, wherein the element is a collimator.
 21. An arrangementaccording to claim 20, wherein the first flexure and the second flexureare spaced at a distance less than half of the length of the collimator.22. An arrangement according to claim 17, wherein the element is areflective.
 23. An arrangement according to claim 17, wherein theelement is a grating.
 24. A beam steering arrangement, comprising: aflexure arrangement in accordance with claim 20; and actuating means forapplying movement to the first flexure so that an actuator movement inany direction causes a collimator movement in the opposite direction,the relative moment of inertia of the actuator and collimator acting tocounterbalance any externally induced movements.
 25. An arrangement inaccordance with claim 24, wherein the actuating means comprises apiezoelectric actuator which when actuated displaces two dimensionally.26. An arrangement according to claim 17, wherein the first flexure islocated upstream from the second flexure.
 27. An arrangement accordingto claim 17, wherein any of the arrangement's components incorporate aslot extending from the periphery to an inward portion of thecomponents, thereby facilitating any one of the ready insertion andremoval of an optical fiber.
 28. An arrangement according to claim 17,wherein any of the flexures comprise a hole sufficient in diameter toallow the passage of an optical fiber and to avoid contact between thefiber and the flexure.
 29. An arrangement according to claim 17, whereinthe support structure comprises an actuator.
 30. An arrangementaccording to claim 17 and extending in the Z-direction, comprising atleast a first and second actuator, the first flexure being at least inpart the extremity of the first actuator which extends in theZ-direction when actuated and the second flexure comprising meanslocated at the extremity of the second actuator for pivoting thecollimator when the first beam is actuated.
 31. An optical switchcomprising an arrangement in accordance with claim 17.